Abstract

Traits are widely used to detect and explain responses of ecosystem processes to environmental changes. Various studies use trait data from databases, often providing one value per trait and species, neglecting intraspecific trait variability along spatio-temporal gradients. Handbooks for standardized trait measurements claim that traits should be measured at an ‘optimal’ stage, which is typically defined to be reached when the plants are in full blossom. However, it is unclear whether this method is appropriate. The main aim of this study was to quantify the extent to which trait values vary with season and phenology, a type of variation that has been overlooked so far relative to other sources of intraspecific variation. Further, we aimed to investigate whether species rankings remain consistent throughout the year.

The results showed that all traits varied significantly throughout the year in a species-specific manner. We detected trait relationships with vegetative but not with flowering phenology. Species rankings were inconsistent throughout the season in all traits.

We concluded that the seasonal timing of trait measurements is crucial. Most notably SLA, Fv/Fm and stomatal size were the most robust traits in terms of small intraspecific and large interspecific variation and showed largely consistent species rankings across seasons.

Notes

Acknowledgements

We would like to thank Patrizia König for helpful comments on the manuscript and Jennifer McCaw for assistance in the field. The research of CR was kindly supported by the German Research Foundation (DFG) project RO 3842/3-1, and the research of MBR was partly supported by the DFG project BE4143/2-1.